In general, it was noticed all over the world that after earthquakes there were changes in the aquifer and in output of the production fields. The earthquakes produce shock waves that are propagating hundreds of miles away from the epicenter. Systematic observations collected from Russian oil fields showed that after earthquakes an increased oil production was recorded. Changes in oil production continued for periods that ranged from several months to three years after the earthquake. This represents clear evidence that the shock waves can play a role in the oil industry.
Shock waves were studied from the beginning of the 20th century for military, medical and civilian applications. The use of shock waves in non-destructive applications was focused towards the middle of the century for the use in the medical field in order to destroy kidney stones from outside the body (extracorporeal treatment). These new devices were invented in Germany and they were called lithotripters. The first lithotripters used the electrohydraulic principle to produce shock waves, which is based on high voltage discharge in between two electrodes submerged in water. The high voltage discharge vaporizes the water and produces a plasma bubble that grows very fast and collapses violently, producing a shock wave that is focused via a reflector towards the desired area. The transformation of the high voltage electric energy into kinetic energy of the shock waves is efficient and proved very beneficial for different medical fields as urology, orthopedics, wound care, etc. After development and commercialization of the electrohydraulic lithotripters, new methods of producing shock waves were researched and implemented based on the electromagnetic or piezoelectric principles.
The idea of using shock waves inside the oil fields started to be incorporated in patents in the late fifties (U.S. Pat. No. 2,871,943) up to now. All these patents describe different constructions to produce seismic waves or the electrohydraulic shock waves that are generated using the high voltage discharge in between two opposing electrodes (known also as spark gap principle—see U.S. Pat. No. 4,074,758, U.S. Pat. No. 4,169,503 and U.S. Pat. No. 6,427,774 B2). The seismic shock waves are difficult to produce and have unpredictable effects on other earth structures, water beds, etc. and can generate uncontrollable environmental issues. The shock waves produced using large magnitude explosive means are also difficult to implement and control, although they produce enough energy to stimulate oil field production.
The electrohydraulic shock waves produced via spark gap electrodes, have problems with maintaining the desired distance between the two electrodes in order to be able produce persistent shock waves (see U.S. Pat. No. 4,074,758, U.S. Pat. No. 4,169,503 and U.S. Pat. No. 6,427,774 B2). The electrodes during high voltage discharge are consumed due to high heat, chemical reactions and corrosion. To address these challenges super alloys were used for the electrodes, which can prolong their life. However, the shock waves devices need to be used for days and weeks, which will require numerous exchanges of the electrodes that make this solution not feasible for field applications. Different feeding mechanisms for electrodes to offset the electrodes consumptions were employed in other patents, with complicated feeding systems and controls, which makes these systems expensive and unpractical too (see U.S. Pat. No. 6,427,774 B2).
Furthermore, a combination of electrohydraulic and electromagnetic generators that produce both acoustic vibration and electromagnetically-induced high frequency vibrations were described in U.S. Pat. No. 6,427,774 B2. The purpose of this dual method is to enhance oil stimulation by overlapping shock waves with electromagnetic waves. The electrohydraulic shock waves described in this patent are generated using spark gap electrodes as well.
Shock waves were also described of being produced using hydraulic means in U.S. Pat. No. 8,113,278 B2. However, these shock waves are radial in nature and are neither focused nor unidirectional, which reduces their efficiency.
The inventions from this patent relate to other ways to produce shock waves utilizing either one or more laser sources, or a self-generated combustible gas supply, or a micro-explosive pellet, and piezocrystals or a piezofiber composite configuration. All of these new approaches are able to offer a high longevity of the shock waves devices, which fits the needs of the oil industry applications.
The shock waves devices can be used in oil industry processes as follows:                Creating an unidirectional and targeted/focused pressure field inside the oil/gas field;        Reducing the drilling time by cracking the rock in front of the drilling head;        Dropping oil viscosity and creating coalescence of small drops of oil due to pressure gradients generated by shock waves;        Enhancing the existing oil extraction technologies, as an adjunct method/process;        Increasing efficiency of the fracking technology;        Reducing the amount of water and high pressures necessary for fracking;        Cleaning and reuse of water used for fracking process, which contributes to environmental protection and reduced costs;        Applying it as independent technology for Improved Oil Recovery (IOR) and/or Enhanced Oil Recovery (EOR)        Operating in combination with other technologies for IOR and/or EOR        Unplugging clogged pipes, oil wells, etc. by eliminating the scales, paraffin and asphaltene formation from inside the pipes/bores;        Unblocking oil pipes that form ice plugs in the arctic regions;        Cleaning the unpiggable pipes for oil transportation or processing installations, through internal or external approaches (depending on the access to the pipes);        Separating of water and solid particulates from extracted oil;        Cleaning continuously the membranes used on the oil processing installation for increased productivity and elimination of down times.        
It is an objective of the present inventions to provide shock wave generating devices that are modular, do not need high maintenance and can, if needed, be used in conjunction with other oil drilling or oil extraction equipment without the need of expanding the well bore diameter or removing the device during drilling or oil extraction.
Furthermore, the shock waves devices employed in oil industry should be high energy devices capable of producing strong shock waves that can penetrate the desired area for long distances and be able to crack the rock formation present in the targeted zone. One or more shock waves devices can be used, which can be placed in one or more well-bores, depending on specifics for each oil field.
The shock waves produced by the proposed devices will have a compressive phase (produces high compressive pressures) and a tensile phase (produces cavitation bubbles that collapse with high speed jets) during one cycle of the pressure pulse. This two synergetic effects work in tandem by acting at macro (compressive phase) and micro level (cavitation jets of the tensile phase), which is enhancing the effects of the shock waves on the well structure and oil incorporated in it.
The shock wave pulses are made up of frequencies ranging from 100 kHz to 20 MHz and will generally have a repetition rate of 1 to 20 Hz. The repetition rate is limited by cavitation, which represents the longest time segment (hundreds to thousands of microseconds) of the pressure pulse. In order to not be negatively influenced by the new coming pulse, the cavitation bubbles need sufficient time to grow to their maximum dimension and then collapse with high speed jets that have velocities of more than 100 m/s. These jets play an important role in cracking the rock, opening pores and making the oil more fluid. Thus, the shock wave pulses that have a high repetition rate can interfere with one another and negatively affect the cavitation period, hence reducing the desired effect of the shock waves.